The present invention relates to an image transmission apparatus and, more particularly, to an image transmission apparatus which can select one of coding schemes suitable for color image data and monochrome image data in units of pages depending on whether a transmission page is constituted by color image data or monochrome image data, when, for example, data having both color and monochrome document data is to be transmitted.
In a conventional apparatus of this type, document data having both color and monochrome document data is transmitted as follows. All the document data is considered either color document data or monochrome document data. The document data is then coded by a color image coding scheme suitable for color document data or a run-length coding scheme suitable for monochrome document data so as to be transmitted depending on whether the document data is considered as color or monochrome document data.
Alternatively, in order to transmit color document data and monochrome document data by different coding schemes, document data is transmitted in two communication cycles.
In other cases, for example, when it is found that an apparatus at the receiving end does not have a color document coding function, after transmission of the document data as color document data is started, the data coded by the monochrome image run-length coding scheme is transmitted again.
The above-described conventional apparatus, however, has the following problems.
(1) If monochrome document data is coded by the color image coding scheme, the following problems are posed when the data is decoded and printed out:
Since a black image is printed in three colors, i.e., red, green, and blue, a high cost is inevitable. PA1 An unnecessary color is output on a white portion. PA1 When a character or the like it printed, color blurring occurs at an edge portion of the character.
(2) If color document data is coded by the monochrome image run-length coding scheme, the color document data can only be transmitted as a monochrome image.
(3) If color and monochrome document data are to be separately transmitted, even though the data can be transmitted in one communication cycle, it requires cumbersome operations, i.e., sorting documents and performing transmission processing twice. In addition, transmission itself involves some cost.
(4) It is only after image communication is actually performed upon line connection that an operator can check which coding scheme an apparatus at the receiving end can handle. Therefore, unless the type of coding scheme which the apparatus at the receiving end can handle is checked in advance, the coding function of the apparatus at the receiving end may differ from the coding scheme used at the transmitting end. As a result, communication and coding processing must be performed again, and hence data transmission cannot be smoothly performed.